Thermal variation of structure and electrical conductivity in Bi14WO24 |
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Authors: | A Borowska-CentkowskaF Krok I Abrahams W WrobelJR Dygas S Hull |
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Institution: | a Faculty of Physics, Warsaw University of Technology, ul. Koszykowa 75, 00-662, Warsaw, Polandb Centre for Materials Research, School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdomc ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom |
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Abstract: | Structure and electrical conductivity of Bi14WO24 as a function of temperature have been examined by X-ray and neutron powder diffraction, a.c. impedance spectroscopy and differential thermal analysis. The room temperature structure was successfully refined using a monoclinic subcell model in space group I2/m. However, additional reflections in the neutron data are consistent with a large supercell of dimensions a = 17.3780(1) Å, b = 17.3891(1) Å, c = 26.1785(2) Å and β = 90.270(1)°, as previously proposed. Transitions to tetragonal and cubic phases are observed at ca. 35 °C and 780 °C, respectively. The structure of the high temperature polymorph is confirmed as a fully disordered δ-Bi2O3 type phase. Analysis of the defect structure is consistent with a predominantly tetrahedral environment for tungsten, as seen at low temperatures. The conductivity behaviour is correlated with the appearance of the δ-phase at high temperatures and exhibits a value of 0.97 S cm− 1 at 800 °C. |
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Keywords: | Bismuth oxide Bismuth tungsten oxide Fluorite Defect structure Neutron diffraction Impedance spectroscopy |
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